In recent years, for the purpose of the global environmental protection and effective utilization of energy resources, power generators have been developed that utilize natural energy such as wind power generation and solar power generation. In addition, such an action has been taken by which generated power obtained by utilizing natural energy is purchased by power companies from private companies.
When the wind power generation or the solar power generation is performed, the generated power fluctuates greatly due to natural conditions such as season or weather. Therefore, a large electricity storage system is installed next to the power generator to absorb fluctuations of the generated power described above, which can supply power to a power system stably. In addition, electric power load is leveled by charging storage batteries at night when the load is light on a demand side and discharging the storage batteries in the daytime when the load is heavy on the demand side.
For example, Patent Document 1 discloses a power storage system including a continuous storage battery and an instantaneous storage battery, and controls switching electric power supply to/from respective storage batteries using a common controller and a common bidirectional inverter.